MC and M23C6 carbides in Armour steel

MC and M23C6 carbides in Armour steel

Table 1: Class 2 armour steel compositions according to MIL MIL-A-11356F and used in experiments.

Figure 1: Microstructure of as-cast specimen. Scale bar: 20 µm.

Figure 2: Microstructures of HAZ of parts single pass welded (a) and pre-heated/single-pass welded (b). Scale bars: 20 µm.

Carbide name: MC, M23C6
Record No.: 1061
Carbide formula: MC, M23C6
Carbide type: MC, M23C6
Carbide composition in weight %: No data
Image type: LM
Steel name: Armour steel
Mat.No. (Wr.Nr.) designation: No data
DIN designation: No data
AISI/SAE/ASTM designation: No data
Other designation: No data
Steel group: Armour steels
Steel composition in weight %: See the table 1.
Heat treatment/condition: In this research, Class 2 armour steel parts were welded using single-pass and pre-heated/single-pass conditions to examine optimal welding parameters in relatively thin parts. Armour steel parts were produced in high frequency induction furnace and cast into resin-bonded sand mould. Specimens were then machined into 5 x 10 x 100 mm dimensions, cut into two pieces (5 x 10 x 50 mm) and gas tungsten arc welded (GTAW) using a low-alloyed high-strength steel filler rod (AWS A5.5:E 8018-B2). Chemical compositions of typical and cast armour steels were given in Table 1. Test parts were welded using 70 A current and 10 l/min argon flow. (A) parts were single pass welded. (B) parts were pre-heated to 100°C and then single pass welded. Welded specimens were investigated using optical microscopy and Vickers hardness tests. Optical micrography was used to characterise transition sites of base metal, HAZ and weld zone. Hardness test was conducted to characterise homogeneity of welding in terms of mechanical properties.
Note: Purpose: In this study, microstructural and mechanical evaluations of class 2 armor steel after single-pass and pre-heated/single-pass welding were investigated to reveal the effect of pre-heating on heat affected zone (HAZ) in thin armor steel parts.
Design/methodology/approach: In this research, class 2 armor steel parts were welded using single-pass and pre-heated/single-pass conditions to examine optimal welding parameters in relatively thin parts. Welded specimens were investigated using optical microscopy and Vickers hardness tests. Optical micrography was used to characterise transition sites of base metal, HAZ and weld zone. Hardness test was conducted to characterise homogeneity of welding in terms of mechanical properties.
Findings: The results have shown that pre-heat/single-pass welding of armor steel could provide homogeneous hardness distribution along welding region. Similar microstructures and mechanical properties were found in base metal and HAZ.
Practical implications: Armor steel was succesfully welded using GTAW without any defects either in weld seam or HAZ.

Segregation is generally inevitable in castings which results in degradation of mechanical properties. Armour steels without annealing have significantly MnS segregated sites. In present study, no heat treatment was conducted in weld region to examine the characteristics of HAZ. Microstructure of as-cast test parts was given in Fig. 1. Previous studies have shown that approximately 2% M23C6 and 0.5% MC carbide formation. Microstructures of HAZ of parts single-pass welded (A) and pre-heated/single-pass (B) were given in Fig. 2a and Fig. 2b. Fine grained microstructure was resulted due to rapid cooling. However higher hardness alone is not a significant property in steels used in armoury equipments since it does not have direct influence in fracture strain.
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Reference: Not shown in this demo version.