Need to increase hardness of 420 weld overlay 1

[amyh33]

A 420 SS overlay is being applied to carbon steel vessel (.35% C) using submerged arc welding. Pre and post weld heat treatment are being used and surface is physically acceptable (no cracking). It takes approximately 3 passes to buildup to desired 3/8" thickness of 420 layer. The desired hardness of completed overlay is 55 Rockwell C - but results are currently 45 - 51 Rockwell C depending on post-weld stress relief temperatures.

We are looking for guidance on suggested methods to increase the overlay surface hardness to consistently achieve 55 Rockwell C. Weld additives and/or tempering are acceptable.

 

[metengr]

Amyh33;
It would appear from your description of the problem that you could be tempering the 420 ss weld deposit during stress relief (post weld heat treatment) of the carbon steel. If you have concerns about having to stress relieve the carbon steel base material, you could try the method below - I would weld a test coupon first to optimize the welding parameters.

1. Butter the carbon steel base material with Inconel weld metal using the rquired preheat, depending on the carbon steel base metal thickness.

2. After the carbon steel is buttered with Inconel 182 (SMAW process) or 82 (if you are using the GTAW process), deposit the 420 ss on top of the butter layer using a 400 deg F preheat with no post weld heat treatment. Keep the interpass temperature below 700 deg F with the 420 ss weld deposit. This way you could achieve the as-deposited hardness of the 420 ss weld with no post weld or stress relief heat treatment cycle. The as-welded 420 ss should be about 55 to 57 HRC.