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.


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