Welding of Medium/High Carbon Steels and Special Steels

1. Introduction

Steel contains Si, Mn, P, and S besides C. These five chemical elements are called the 5 chemical elements of steel. Steel that contains 0.3% or less of C is called low−C steel or mild steel. Steel with 0.6% or more of C is called high−C steel. For instance, carbon tool steel is in this grade. Steel with 0.3～0.6% of C is called medium−carbon steel. Machine structure steel is in this grade. Special steel is of such a grade that contains, besides the 5 elements, higher Mn as compared with carbon steel, or such alloying elements as Ni, Cr, and Mo are also added for its intended use.

The JIS standard classifies iron and steel materials as in Table 1, in which steel is divided into plain steel, special steel and steel castings. Special steel is further divided into high strength steel, tool steel, and special−use steel. Typical steel grades of medium−carbon steel and special steel are as shown in Tables 2～3. These tables include the AISI/SAE steel grades and ASTM specifications that are similar to the JIS steel grades.

Table 1 Classification of iron and steel materials as per the JIS standard, supplemented with ASTM/AISI/SAE

1st class.	2nd class.	3rd class.	Typical JIS grades (ASTM/AISI/SAE)*1
Iron and Steel	Plain steels	Steels for structure or pressure vessel	JIS G3101 : SS, JIS G3103 : SB, JIS G3104 : SV, JIS G3106 : SM (ASTM A36, A204, A285, A31, A283, A529)
	Special steels	Carbon/alloy steels for structure	JIS G4051 : S××C, JIS G4053 : SCr, SMn, SMnC, SCM, SNC, SNCM, JIS G4202 : SACM, JIS G3119 : SBV, JIS G3120 : SQV (AISI/SAE : 1010~1060, 5120~5140, 1522~1541, 4130~4147, 8615~8640, 4320~4340, ASTM A302, A387, A533, A734)
		Tool steels	JIS G4401 : SK, JIS G4404 : SKS, SKD, SKT, JIS G4403 : SKH (AISI/ASTM : W1−11~1−8, F2, L6, W2, D3~H 19, T1~M42)
		Steels for special uses	JIS G4303~4321 : SUS, SUH, JIS G4805 : SUJ, JIS G4801 : SUP, JIS G4804 : SUM (AISI : 201~444, 309~446, 52100, 9260~4161, 1212~1144, etc.)
	Steel castings	Carbon/alloy steel castings	JIS G5101 : SC, JIS G5102 : SCW (ASTM A27, A216)
		Carbon/alloy steel castings for structure	JIS G5111 : SCC, SCMn, SCSiMn, SCMnCr, SCMnM, SCCrM, SCMnCrM, SCNCrM (ASTM A148)
		Steel castings for special uses	JIS G5121 : SCS, JIS G5122 : SCH, JIS G5131 : SCMnH (ASTM A743, A744, A351, A297, A447, A608, A128)
	Steel forgings	Carbon steel forgings	JIS G3201 : SF (ASTM A105, A668)
		Carbon/alloy steel forgings for structure	JIS G3203 : SFVA, JIS G3202 : SFVC, JIS G3204 : SFVQ (ASTM A182, A336, A105, A181, A266, A508, A541)
	Iron castings	Gray iron castings	JIS G5501 : FC (－)
		Spheroidal graphite iron castings	JIS G5502 : FCD (ASTM A536)
		Malleable iron castings	JIS G5705 : FCMB, FCMW, FCMP (－)
(Note) *1. For ASTM, only the specification No. is listed for reference ; hence, the exact steel grade comparable to the JIS grade should be studied in the relevant specification.

Table 2 Carbon steels for machine structural use (Excerpted from JIS G 4051−1979 and supplemented with AISI/SAE)

JIS grade (AISI/SAE)*4	Chemical composition(%)			General mechanical properties*1			Carbon*2 equivalent	Weldability*3
	C	Mn	Si	Tensile strength (MPa)	Elongation (%)	Hardness (Vickers)
S30C(1030)	0.27~0.33	0.60~0.90	0.15~0.35	≧540	≧23	160~225	0.44	△
S33C(－)	0.30~0.36	0.60~0.90	0.15~0.35	－	－	－	0.47	△
S35C(1035)	0.32~0.38	0.60~0.90	0.15~0.35	≧570	≧22	175~250	0.49	△
S38C(1038)	0.35~0.41	0.60~0.90	0.15~0.35	－	－	－	0.52	×
S40C(1039,1040)	0.37~0.43	0.60~0.90	0.15~0.35	≧610	≧20	190~270	0.54	×
S43C(1042,1043)	0.40~0.46	0.60~0.90	0.15~0.35	－	－	－	0.57	×
S45C(1045,1046)	0.42~0.48	0.60~0.90	0.15~0.35	≧690	≧17	210~285	0.59	×
S48C(－)	0.45~0.51	0.60~0.90	0.15~0.35	－	－	－	0.62	×
S50C(1049)	0.47~0.53	0.60~0.90	0.15~0.35	≧740	≧15	228~295	0.64	×
S53C(1050,1053)	0.50~0.56	0.60~0.90	0.15~0.35	－	－	－	0.67	×
S55C(1055)	0.52~0.58	0.60~0.90	0.15~0.35	≧780	≧14	240~305	0.69	×
S58C(1059,1060)	0.55~0.61	0.60~0.90	0.15~0.35	－	－	－	0.72	×
(Note) *1. General mechanical properties are for quenched and tempered steels. *2. The carbon equivalent (Ceq) was calculated by the following equation. 　　 *3. The marks for weldability signify as follows : △：Fairly difficult ×：Extremely difficult *4. For chemical composition, mechanical properties, carbon equivalent, and weldability, refer to the relevant AISI/SAE specification.

Table 3 Cr−Mo steels for machine structural use (Excerpted from JIS G 4053−2003 and supplemented with AISI/SAE)

JIS grade (AISI/ SAE)*4	Chemical composition(%)					Tensile test		Brinell hardness	Heat treatment(℃)		Carbon*2 equivalent	Weldability*3
	C	Si	Mn	Cr	Mo	Tensile strength (MPa)	Elongation (%)		Quenching	Tempering
SCM415 (－)	0.13 ~0.18	0.15 ~0.35	0.60 ~0.90	0.90 ~1.20	0.15 ~0.25	≧830	≧16	235 ~321	1st 850~900 Oil cooling 2nd 800~850 Oil cooling	150~200 Air cooling	0.56	△
SCM418 (－)	0.16 ~0.21	0.15 ~0.35	0.60 ~0.90	0.90 ~1.20	0.15 ~0.25	≧880	≧15	248 ~331	1st 850~900 Oil cooling 2nd 800~850 Oil cooling	150~200 Air cooling	0.59	△
SCM420 (－)	0.18 ~0.23	0.15 ~0.35	0.60 ~0.90	0.90 ~1.20	0.15 ~0.25	≧930	≧14	262 ~352	1st 850~900 Oil cooling 2nd 800~850 Oil cooling	150~200 Air cooling	0.61	△
SCM421 (－)	0.17 ~0.23	0.15 ~0.35	0.70 ~1.00	0.90 ~1.20	0.15 ~0.25	≧980	≧14	285 ~375	1st 850~900 Oil cooling 2nd 800~850 Oil cooling	150~200 Air cooling	0.62	△
SCM430 (4130)	0.28 ~0.33	0.15 ~0.35	0.60 ~0.90	0.90 ~1.20	0.15 ~0.30	≧830	≧18	241 ~302	830~880 Oil cooling	550~650 Rapid cooling	0.71	×
SCM432 (－)	0.27 ~0.37	0.15 ~0.35	0.30 ~0.60	1.00 ~1.50	0.15 ~0.30	≧880	≧16	255 ~321	830~880 Oil cooling	550~650 Rapid cooling	0.71	×
SCM435 (4137)	0.33 ~0.38	0.15 ~0.35	0.60 ~0.90	0.90 ~1.20	0.15 ~0.30	≧930	≧15	269 ~331	830~880 Oil cooling	550~650 Rapid cooling	0.76	×
SCM440 (4140, 4142)	0.38 ~0.43	0.15 ~0.35	0.60 ~0.90	0.90 ~1.20	0.15 ~0.30	≧980	≧12	285 ~352	830~880 Oil cooling	550~650 Rapid cooling	0.81	×
SCM445 (4145, 4147)	0.43 ~0.48	0.15 ~0.35	0.60 ~0.90	0.90 ~1.20	0.15 ~0.30	≧1030	≧12	302 ~363	830~880 Oil cooling	550~650 Rapid cooling	0.86	×
SCM822 (－)	0.20 ~0.25	0.15 ~0.35	0.60 ~0.90	0.90 ~1.20	0.35 ~0.45	≧1030	≧12	302 ~415	1st 850~900 Oil cooling 2nd 800~850 Oil cooling	150~200 Air cooling	0.68	×
(Note) *2. The carbon equivalent (Ceq) was calculated by the following equation. *3. The marks for weldability signify as follows : △：Fairly difficult ×：Extremely difficult *4 For chemical composition, mechanical properties, heat treatment, carbon equivalent, and weldability, refer to the relevant AISI/SAE specification.

2. Fundamental considerations for selection of welding consumables

The basic considerations for selection of welding consumables are described at first. The mechanism of crack generation and its prevention will be described later.

In the first place, the welding consumables with much diffusible hydrogen in the weld metal (such as the ilmenite type electrode and lime−titania type electrode) should never be used for welding medium/high carbon steels and special steels. It is a must to use the low−hydrogen type welding consumables.

In the second place, the strength of the weld metal must be considered.

Medium/high carbon steel can generally be characterized by high strength, the tensile strength of which often surpasses 1000MPa. When welding such a high strength steel material, there are two ways of thinking in selecting the welding consumables. One is to place importance on the strength of the weld metal and adopt such a welding consumable that produces the weld metal whose strength is similar to that of the base metal. The other is to place more importance on the crack resistance of the weld metal than on its strength.

Generally speaking, when other conditions are the same, the crack resistance of a weld joint becomes better as the strength of the weld metal becomes lower. In other words, there is a higher risk of crack occurrence as the strength of the weld metal is higher.

Therefore, upon selection of the welding consumables, it is necessary to carefully examine whether or not the strength of the weld metal need to be comparable to that of the base metal. It should be noted to select, where it is possible, a welding consumable with a lower strength as much as possible to decrease the risk of crack occurrence.

The following table of recommended welding consumables gives two cases of recommendation : one is the case where just joining is required and the other is the case where the weld metal needs to have a similar strength as the base metal.

Even though the table of recommended welding consumables does not refer to it, there is a case where 309−type austenitic stainless steel welding consumables are recommended for welding medium/high carbon steels.

This recommendation comes from the fact that a big cause of cracks in the weld joint of medium/high carbon steel is the hardening of HAZ and diffusible hydrogen in the weld metal.

Of course, the weld HAZ can be hardened even if austenitic stainless steel welding consumables are used. But absence of diffusible hydrogen in the weld metal is considered to contribute to crack resistance together with stable structure of the weld metal.

Hence, where it is impossible to apply preheating or where there is no problem of thermal fatigue due to difference of thermal expansion coefficient, austenitic stainless steel welding consumables may be used.

Steel grade*1		Preheat temp. (℃)	Recommended welding consumables
JIS	ASTM or AISI/SAE		For joining only			For joining with near−base−metal strength
			Shielded metal arc welding	MAG welding	TIG welding	Shielded metal arc welding	MAG welding	TIG welding
S30C,33C	1030	100min.	LB−47 LB−26	MG−50 MIX−50S	TG−S50	LB−52	MG−50 MIX−50S	TG−S50
S35C	1035	100min.				LB−62	MG−60 MG−S63B	TG−S62
S38C,40C, 43C	1038,1039 1040,1042 1043	150min.				LB−62	MG−60 MG−S63B	TG−S62
S45C,48C, 50C	1045,1046 1049	200min.				LB−106	MG−70 MG−S70	TG−S80AM
S53C	1050, 1053	250min.				LB−106	MG−70 MG−S70	TG−S80AM
S55C	1055	250min.				LB−116	MG−80 MG−S80	TG−S80AM
S58C	1059, 1060	300min.				LB−116	MG−80 MG−S80	TG−S80AM
SNCM220, 420	8615,8617 8620,8622	200min.				LB−116	MG−80 MG−S80	TG−S80AM
SNCM431	－	300min.				LB−116	MG−80 MG−S80	TG−S80AM
SNCM439, 447,630	4340	350min.				CM−A106	MG−S2CM	TG−S2CM
SCM420	－	250min.				CM−A106	MG−S2CM	TG−S2CM
SCM430, 435	4130, 4137	300min.				CM−A106	MG−S2CM	TG−S2CM
SCM440, 445	4140,4142 4145,4147	350min.				CM−A106	MG−S2CM	TG−S2CM
SCM822	－	250min.				CM−A106	MG−S2CM	TG−S2CM
SF390A, 440A,490A	A105 A668 : B,C	150min.				LB−52	MG−50 MIX−50S	TG−S50
SC360, 410,450,480 SFVC−1, 2A,2B	A27 (See below for A105, A181, A266)	100min.				LB−52	MG−50 MIX−50S	TG−S50
SF540A, 590A	A668 : D,Fb	200min.				LB−62	MG−60 MG−S63B	TG−S62
－	A181−60 A266−1	100min.	－	－	－	LB−47 LB−26	MG−50 MIX−50S	TG−S50
－	A105 A181−70 A266−2,4	100min.	－	－	－	LB−52	MG−50 MIX−50S	TG−S50
－	A266−3	100min.	－	－	－	LB−57	MG−60 MG−S63B	TG−S62
*1. Check the mechanical properties of the filler metal are acceptable to the application in advance.

Page Top