Ferrite content in stainless steel and embrittlement

Summary the important notes on this concept: SS will be 885*F (475*C) embrittlement and, or sigma-phase promotion by Ferrite content. The ferrite contained in Austenite SS is kept around 2-5% for weldability. The Embrittlement by Sigma phase is prevented by keep FN < 10 The Embrittlement by 475*C is prevented by keeping FN <14 Example: Some refinery specs required FN on SS347 <9 to prevent the Embrittlement (475*C Embrittle + Sigma phase embrittle)   There are a number of different types of steels that may be referred to as ‘stainless’; previous articles have considered ferritic and precipitation hardening steels for … Continue reading Ferrite content in stainless steel and embrittlement

Austenite Stainless Steel at high-temperature (embrittlement)

The phenomenon of embrittlement in austenitic stainless steel welds exposed to high temperature is accelerated by the presence of delta ferrite. To avoid solidification cracking in austenitic stainless steel welds, the composition of the filler material must be optimized to ensure that there is some delta ferrite present in the weld metal (typically >3%). However, delta ferrite transforms into intermetallic phases, notably the sigma phase, faster than austenite either during high-temperature service or during post-weld heat treatment (PWHT). Sigma phase is an intermetallic with an approximate chemical formula FeCr and, as with most intermetallics, it is very brittle and hence … Continue reading Austenite Stainless Steel at high-temperature (embrittlement)

Duplex piping and seawater

22%Cr duplex stainless steels are not suitable for elevated temperature unprotected seawater applications because they suffer from the crevice and pitting corrosion at even moderate temperatures. Super duplex stainless steels present superior corrosion resistance to duplex stainless steels in seawater applications, and provided weld quality is maintained, pitting should not occur in seawater up to about 40°C. The operational limit stipulated in the Norsok Standard (M-001, Rev.2, November 1997) is one of the most conservative for unprotected super duplex service and is more restrictive than most operators’ own requirements. The maximum operating temperature is set at 15°C and the maximum … Continue reading Duplex piping and seawater

Stainless steel discolour (sugaring) in welding

We receive several calls about welding stainless and the beautiful rainbow colors, or lack thereof, on the weld and heat-affected zone.  Is the tinting an indication of quality?  Are these colors acceptable? Do they show that the weld had enough heat to penetrate?  Why do they need to be cleaned?  The questions are endless. If you are one of the thousands that base their quality standards on Instagram posts please stop right now.  All the beautiful pictures of stainless welds are emphasizing the beauty of the rainbow colors in GTAW and GMAW welds.  This is producing a false expectation and the impression that … Continue reading Stainless steel discolour (sugaring) in welding

What is Welding Preheating ?

The phenomenon of heating the joint in the weld zone before the commencement of welding procedure is known as pre-heating. Normally it is applied by the use of ovens, flame producing torch, resistive heating elements and high frequency heating elements. It helps to eliminate welding interruption and several imperfections and set the joining phenomenon on smooth track. Why to use Pre-heat ? Following are the main reasons for using the pre-heat in a welding procedure. The use of Pre-heat, eliminates the surface moisture; consequently reducing the hydrogen induced cracking. It tweaks fusion and deposition of weld metal in a better … Continue reading What is Welding Preheating ?

Stainless Steel Material In Sea Water

Other Topic: Duplex piping and seawater With this topic we will discuss about Corrosion resistance of Austenitic stainless steel in Sea water. 1) Sea water: Seawater is water from a sea or ocean. Sea water in the world’s oceans has a salinity of approximately 3.5%, or 35 parts per thousand. This means that for every 1 litre (1000 mL) of seawater there are 35 grams of salts (mostly, but not entirely, sodium chloride) dissolved in it. Although a vast majority of seawater is found in oceans with salinity around 3.5%, seawater is not uniformly saline throughout the world. 2) Chlorides: The … Continue reading Stainless Steel Material In Sea Water

ALLOY ELEMENT AFFECTION IN STEEL PROPERTIES

If you are in steel industry, have you ever notice what all those chemical composition listed on a steel materials test report really mean? You may only know different steel grade has many different chemical composition and elements in different amount. Here in this post, we sort out and list 21 chemical elements and effects on steel properties. 21 Chemical Elements and Effects on Steel Mechanical Properties Steel in general is an alloy of carbon and iron, it does contain many other elements, some of which are retained from the steel making process, other elements are added to produce specific properties. … Continue reading ALLOY ELEMENT AFFECTION IN STEEL PROPERTIES

Stainless Steel Material: what is pickling / passivation?

Stainless Steel material: ( refer to other topic: what is stainless steel? ) A metallic alloy (i.e., metal made of multiple elements such as chromium, nickel, and molybdenum) is generally considered to be “stainless” when its chromium content is greater than about 12 percent by weight ( some document mention it is about 10.5% chromium ), with the balance being iron, higher alloyed stainless steels have higher levels of chromium. Chromium provides corrosion resistance to these alloys by forming a thin, adherent, corrosion-resistant oxide film on a clean (e.g., pickled, wire/rotary brushed, or ground) surface (of the alloy). The main … Continue reading Stainless Steel Material: what is pickling / passivation?

Why Stainless steel rust / corrosion? – Part 2 – Other corrosion.

In Part 1, we know about Pitting corrosion. We will continue with remain one: 2) Crevice ( gap ) corrosion– Stainless steel requires a supply of oxygen to make sure that the passive layer can form on the surface. In very tight crevices, it is not always possible for the oxygen to gain access to the stainless steel surface thereby causing it to be vulnerable to attack. Crevice Corrosion refers to the localized attack on a metal surface at, or immediately adjacent to, the gap or crevice between two joining surfaces. The gap or crevice can be formed between two metals or a … Continue reading Why Stainless steel rust / corrosion? – Part 2 – Other corrosion.