420 Stainless Steel Bar

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Steel Type – Martensitic

VAL2B is a 12% Chromium martensitic stainless with a medium Carbon content capable of high hardness after heat treatment together with a moderate corrosion resistance.

Designations

VALBRUNA
VAL2B
AISI
420
W.N.
1.4028
UNS
S42000
EN
X30Cr13
BS
420S45

Specifications

ASTM
A276
EN
10088-3

Chemical Composition

Min.
Value %
C
0.28%
Mn
-
Si
-
P
-
S
-
Cr
12%
Max.
Value %
C
0.35%
Mn
1%
Si
1%
P
0.04%
S
0.03%
Cr
14%

Applications

All applications where both hardness and corrosion resistance are indispensable, such as dental and surgical instruments, parts of brakes, valve seats, plastic molds, parts of pumps, pump shafts, wear resistant devices and table cutlery. This grade after hardening and low temperature tempering provides a hardness higher than that of VAL1 and VAL2A.

Machinability

Micro-resulphured VAL2B in the annealed condition, and in the high temperature tempered after hardening condition, offers a good machinability. It’s important to know that the productivity gain depends on the type of machines used, the kind of tools used and their geometry, cutting fluids and the kind of machine operations on the pieces produced. The grinding and polishing of hardened + tempered material at maximum values of hardness must be carried out with great care, in order to avoid the overheating of the surface of the piece resulting in poor corrosion resistance and/or grinding cracks.

Mechanical Properties

CONDITION
Annealed
Subtype
A
Rm [N/mm²]
800 max.
Rm [Ksi]
116 max.
HBW
245 max.
Rp0.2% [N/mm²]
-
Rp0.2% [Ksi]
-
A5D [%]
-
CONDITION
Hardened and Tempered
Subtype
QT850
Rm [N/mm²]
850-1000
Rm [Ksi]
123 - 145
HBW
-
Rp0.2% [N/mm²]
650 min.
Rp0.2% [Ksi]
94 min
A5D [%]
10 min.

Physical Properties

Density
SI / Metric Units
7.7 kg/dm³
US / BS Imperial Units
0.278 lb/in³
Specific Thermal Capacity 20° C
SI / Metric Units
460 J/(kg·K)
US / BS Imperial Units
0.11 Btu/lb°F
Thermal conductivity 20° C
SI / Metric Units
30 W/(m·K)
US / BS Imperial Units
208.004 Btu in/ ft² h °F
Thermal expansion 20° - 100° C
SI / Metric Units
10.5 (10⁻⁶/K)
US / BS Imperial Units
5.833 (10⁻⁶/°F)
Electrical Resistivity 20° C
SI / Metric Units
0.65 Ω·mm²/m
US / BS Imperial Units
25.591 μΩin
Modulus of Elasticity 20° C
SI / Metric Units
215 GPa
US / BS Imperial Units
31183.114 ksi

Heat Treatment

Annealed
Condition
A
Minimum temperature °C
745
Maximum temperature °C
825
Cooling
Air
Hardened
Condition
H
Minimum temperature °C
950
Maximum temperature °C
1050
Cooling
Air
Tempered
Condition
T
Minimum temperature °C
625
Maximum temperature °C
675
Cooling
Air

Weldability

This process for martensitic stainless grades is always risky and a special care must be applied in the choice of welding parameters. In any case, if a welding process were required, a preheating is mandatory and the part must be maintained at temperature and followed by immediate annealing or tempering. Fillers of the same composition can be used to obtain mechanical properties close to that of the base metal. Alternatively, austenitic fillers may be used considering an inevitable reduction of these properties. In solid state joining such as Friction Welding, VAL2B provides a quality bond line. When friction welded with different grades, a tempering or annealing of the welded piece must be done in order to soften the martensitic structure of HAZ and bond line.

 

Cold Working

In the annealed condition, this grade is suitable for cold forming operations such as cold heading or up-setting. It should be pointed out that VAL2B is prone to surface decarburization: a protective atmosphere should be considered in the heat treatment of finished pieces.

Hot Working

Blooms and ingots require a suitable preheating to avoid cracks and a slow cooling in the furnace after forging. Overheating must always be avoided, in order to reduce the risk of internal bursts. An improper cooling could result in stress cooling cracks. Large forgings and large cross – section shapes should be left to cool until their core reaches room temperature and, then, immediately heat treated. A right and suitable heat treatment of pieces after the forging process creates a structure with no or little retained austenite, avoiding delayed cracks.

Heat Treatment

VAL2B should be double tempered after hardening in order to reduce or avoid retained austenite obtaining high values of hardness. Double tempering is not normally used in cutlery production where a single one should be sufficient.

Melting Practices

EAF + AOD